1. Field of the Invention
The present invention relates to a fuel cell stack comprising a plurality of fuel cell units each composed of an electrolyte interposed between an anode electrode and a cathode electrode, the plurality of fuel cell units being stacked with separators intervening therebetween.
2. Description of the Related Art
For example, the solid polymer type fuel cell comprises a fuel cell unit including an anode electrode and a cathode electrode disposed opposingly on both sides of an electrolyte composed of a polymer ion exchange membrane (cation exchange membrane) respectively, the fuel cell unit being interposed between separators. Usually, the solid polymer type fuel cell is used as a fuel cell stack comprising a predetermined number of the fuel cell units and a predetermined number of the separators which are stacked with each other.
In such a fuel cell, a fuel gas such as a hydrogen-containing gas, which is supplied to the anode electrode, is converted into hydrogen ion on the catalyst electrode, and the ion is moved toward the cathode electrode via the electrolyte which is appropriately humidified. The electron, which is generated during this process, is extracted for an external circuit, and the electron is utilized as DC electric energy. An oxygen-containing gas such as a gas containing oxygen or air is supplied to the cathode electrode. Therefore, the hydrogen ion, the electron, and the oxygen gas are reacted with each other on the cathode electrode, and thus water is produced.
In order to supply the fuel gas and the oxygen-containing gas to the anode electrode and the cathode electrode respectively, a porous layer such as porous carbon paper having conductivity is usually interposed at the catalyst electrode layer (electrode surface) by the aid of the separator. One or a plurality of gas flow passages designed to have a uniform widthwise dimension are provided on the mutually opposing surface of each of the separators.
For example, as shown in FIG. 10, a fuel cell stack disclosed in U.S. Pat. No. 5,547,776 has an opening 2 for oxygen-containing gas and an outlet opening 3 which are formed to penetrate through a plate 1. A plurality of flow passage grooves 5a to 5f, which make communication between the opening 2 and the outlet opening 3, are formed in a meandering manner on a surface 4 of the plate 1.
Since the flow passage grooves 5a to 5f meander in the surface 4, a plurality of bent sections 6 are provided corresponding to the both sides of the plate 1. However, at the bent section 6, the curvature is considerably small for the inner flow passage grooves 5f, 5e, although the outer flow passage groove 5a has a relatively large curvature.
Therefore, the pressure loss differs between the inner side (side of the flow passage groove 5f) and the outer side (side of the flow passage groove 5a) of the bent section 6 and it is difficult for the gas to flow on the inner side. For this reason, the gas flow rate is conspicuously lowered especially at the flow passage grooves 5f, 5e disposed on the inner side. As a result, it is difficult to remove the produced water from the flow passage grooves 5f, 5e. A problem is pointed out in that if the produced water is accumulated in the porous layer, then the diffusion performance is lowered for the fuel gas and the oxygen-containing gas to diffuse to the catalyst electrode layer, and the power generation performance is conspicuously deteriorated.
A principal object of the present invention is to provide a fuel cell stack which makes it possible to effectively improve the gas flow performance in the surface of a separator and which makes it possible to ensure satisfactory drainage performance with a simple arrangement.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.